No access to server-side primitives in _middleware.ts? Alternatives?

[sgharms]

Hi there. I'm looking at a project that uses a custom server (boo! hiss) and I'm exploring migrating to Next's middleware instead.

I've found that I can do most things (header mangling, redirects, /api-short-circuiting nextUrl.pathname behavior), but an obvious case that I would have expected to work out of the box is....writing to a file. Let's say I wanted to return the (Next)Response generated in the middleware interaction:

import fs from 'fs';

/* Request handling; response preparation */

fs.writeFileSync('/tmp/razzle.txt', Object.keys(preparedResponse).join('*'));

Error: Module not found: Can't resolve 'fs'

I think I understand what's going on here, 'fs' is not available to client-side code.

The Edge Runtime has some restrictions including:

Native Node.js APIs are not supported. For example, you can't read or write to the filesystem

-- https://nextjs.org/docs/api-reference/edge-runtime#unsupported-apis

OK, I get that, but a middleware isn't exactly a client-side thing. At the basis, I would expect that a middleware provides me access to the request, the response, and whatever other APIs I choose to use. Consider a canonical middleware use case: logging request paths and responses. If I don't have access to fs, net.Socket, etc. , how could that ever be implemented?

Searching the vercel/examples, there was no example. Anyone have a pattern on this?